Structure and role of biological communities involved in the transport and transformation of persistent pollutants at the marine air-water interface (AIRWIN)

Projektdetails

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EU-Beitrag:

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CSC - Cost-sharing contracts

Ziel

The aim of the project is to investigate the structure of biological communities living and growing in the sea surface microlayer (SML), and their role in the transport and cycling of natural organic matter and xenobiotics. This research proposal will provide original data on the identification of organisms living in the SML. It will provide both scientific and biotechnological communities with a collection of organisms with information on:i) their role in the transformation of specific pollutants and;ii) their capacity to produce molecules such asantioxydants which may be used for pharmaceutical applications. The sensitivity of SML organisms to different categories and concentrations of toxic compounds will be assessed to determine if they are suitable bioindicators of atmospheric pollution.The AIRWIN Project provide significant information on the structure and functioning of the sea surface microlayer (SML) as well as a collection of environmental bacterial strains. The SML occurs at least 30-40% of the time at the open global ocean, but its occurrence can be higher in coastal regions were wind speeds are lower. In the Mediterranean Sea, the SML occurs mainly from late spring to early fall and, therefore, is a compartment to be taken into account from the standpoint of the inhabiting biological communities and their role in the transport and cycling of natural organic matter and xenobiotics. An original and interesting result was the comparison of microbial food webs operating at the surface microlayer with those operating in underlying waters. Recommendations were addressed for optimizing the sampling of the surface microlayer. We showed that both, bacterial and phytoplanktonic cells, accumulate in the surface microlayer by the passive and physical process of flotation, with an important part of senescent cells associated with degraded pigments. This interesting result address new questions on the potential influence of the surface microlayer on satellite data used to estimate primary production at the oceanic scale and this should be investigated in the future in different oligotrophic areas of oceans where contrasting situations may be encountered in the pigment concentration of SML and subsurface layers. The surface microlayer of the sea represents the boundary layer between the atmosphere and the sea. There, hydrophobic compounds are accumulating, both naturally occurring and of anthropogenic origin.

Microorganisms present in this layer are degrading these compounds along with ultraviolet radiation (UVR). Although we shown that a lot of bacterial species have developed very efficient mechanisms for DNA repair and if we except a few highly resistant species which were isolated in the SML, the bacterioneuston are apparently not specifically adapted to these high radiation levels. From an evolutionary point of view, it seems likely that this particular microenvironment is sufficiently stable to allow the development of specific (i.e., endemic) microbial communities. Thus, there is no indication that microorganisms inhabiting this microhabitat are specifically suited to degrade anthropogenically introduced compounds. It appears that solar radiation is more efficient in cleaving aromatic or hydrophobic compounds in this microlayer than the neuston biota. Therefore, anthropogenic compounds potentially introduced to the surface microlayer via the atmosphere or via direct release into the sea should be designed to be photosensitive so that they can be photolytically cleaved. An important collection of environmental bacterial strains was developed and more than one hundred of different bacterial species were isolated, purified and stored in this collection. This collection represents an interesting output of the project for the European community at the time of development of genomic and proteomic studies. Some of these species should be of interest for biotechnological and bioremediation applications but this need further investigations to better characterize their physiological and metabolic properties.

The field work carried out within AIRWIN has demonstrated the enrichment of organic contaminants (e.g. PCBs, PAHs, NP, etc.) and heavy metals (e.g. Pb, Cu and Zn) in the sea surface microlayer, as an organic carbon driven process, both in the dissolved and particulate phases. In this respect, the trophic status of the coastal waters will determine the partitioning of xenobiotics between the particulate, colloidal and truly dissolved phases, which has important implications in assessing the corresponding bioavailability. POC explains the SML enrichment of PCBs and organochlorinated pesticides, which tends to be higher than in the dissolved phase. However, for the PAHs higher enrichments were found, suggesting that PAH partitioning is constrained not only by the organic carbon content of the particles but also by the particular form of this carbon. Presumably, soot carbon concentrations are higher in the SML due to accumulation of atmospherically deposited aerosol in the SML. The occurrence of SML seems to be a very important driver enhancing dry deposition fluxes. This is true mainly for accumulation mode aerosols. The effect of a SML with lower surface tension and higher hydrophobicity would enhance the collision efficiency of aerosols to the air-water interface. The field work, in combination with the modelling task, has evidenced that coastal regions are characterized by important net volatilization fluxes of POPs such as PAHs, NPs and PCBs. Conversely, net absorption fluxes are observed at open sea.